Anyone cut off their top tube?

Very risky, the bike can collapse. The frames forum a triangle and if you remove one it will no longer be and collapse.........Curt
 
BMX builds I've seen the top tube is cut, redesigned to fit over the engine then welded back in.
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A fellow member is doing a midframe pocket bike engine build on a BMX.

It's a very tight fit.

However, all the tubes and stays will remain unmolested.

So far, the only welding to the bike will be a triangulated brace from the bottom tube to the motor mount.
 
It depends where and how the engine is mounted.

Yes, I've seen instances in old board track racers, where the engine block braced two sections of the frame's down tube.

However, the bike's top tube was intact.

FWIW, I ran an electric hub, rear friction drive, and front and rear friction drives on a girlie cruiser.

It had no top tube, but the bottom tube was heavily braced.

When loaded to 6 SLA lead batteries, I could literally FEEL! the bike's frame twisting, ever so slightly.
 
Very few BMX frames will allow you to do a mid frame mount without frame modifications.
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A rear mount is probably the best option without modifying the frame.
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Well I just picked up a 16" kids bike. I should be able to cut off the top tube now right? The frame is so small
 

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5-7HEAVEN said:
My opinion, that's a "Dead Man's" choice.

Unsafe at any speed.

Even a 20" bike would be squirrelly to handle above jogging speed.
(Ask me how I know that.)

I'd choose at least a 24" bike.
Click to expand...
That's a bike with 24" wheels. A 24" frame would be for a person over 6' tall.
 
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